J/AJ/99/1831 J/AJ/99/1831 M 68 BVRI photometry G Alcaino W Liller F Alvarado E Wenderoth Astron. J. 99 1831 1990 1990AJ.....99.1831A Clusters, globular Photometry, CCD We present BVRI photometry of the low metallicity globular cluster M68 (NGC 4590) observed with a CCD camera and the 2.2m telescope at ESO/La Silla, and have compared our BV color-magnitude diagrams with the observational results of a previous research. At magnitudes V<22, our BV results, obtained using the INVENTORY code, are in very close agreement with those of the other authors who used DAOPHOT in their reductions. At fainter levels, selection effects appear to affect INVENTORY more than DAOPHOT. We find that V_TO-HB_=3.42+/-0.10, in accord with values found for other clusters. The comparison between our four-color observations and the theoretical isochrones consistently yield a cluster age of 13Gyr with a likely external uncertainty of 2 or 3Gyr. Our derived values for the interstellar reddening at longer wavelengths are generally in agreement (+/-0.02mag) with what would be expected assuming E(B-V)=0.07mag and (m-M)_V_=15.25.

M 68NGC 459012 39 27.9-26 44 35

Star Star number -- Saw Sawyer Hogg name (1973PDDO....3....6S) --- Xpos X position number=2 1 pix = 0.36 arcsec. The origin of (X, Y) coordinates is located at the bottom right. pix Ypos Y position number=2 1 pix = 0.36 arcsec. The origin of (X, Y) coordinates is located at the bottom right. pix Vmag V magnitude mag B-V B-V colour index mag V-R V-R colour index mag R-I R-I colour index mag V-I V-I colour index mag B-I B-I colour index mag Marie-Jose Wagner, Patricia Bauer CDS 1997May16 UNKNOWN UNKNOWN Prepared via OCR at CDS. J_AJ_99_1831.xml